FORCE & MOTION

"There are children playing in the streets who could solve some of my top problems in physics, because they have modes of sensory perception that I lost long ago".

 J.Robert Oppenheimer: commonly known as the father of the atomic bomb 

INTRODUCTION

Many people ask why do I need physics for self defence, firstly you may be able to bore someone to death with it (in my experience it always works especially well on hot chicks) or alternatively you could use physics to analyse forces and motion and determine which techniques give the best or least impact force for striking and blocking, the greatest torque for locking or destroying joints or the greatest momentum when throwing.
As per the quote above most people don't realise they solve very complex physics problems every day. Physics is just the language to describe force and motion, when you throw a ball through a basket ball hoop you have learned by repetition to predict the trajectory of an object, this is actually a physics problem known as projectile motion which has many scary formulae. You solve the same problem every time you punch, kick, strike or block an opponent. At about this point my students and training partners always ask: "If we already solve these problems why do we need to learn physics"? The physics allows us to measure or compare, thereby making better decisions regarding techniques and training, rather than years of repetition we can use a formulae and theory to  understand the underlying principles and concepts. Understanding and applying these concepts and principles whilst training then ensures every repetition of a technique can be self analysed and improved; training time is thus made more efficient and if you have a different body type to your instructor or have disabilities, you can modify the techniques to suit you or the situation at hand. 

I have done and continue to practice many martial arts and one of the greatest frustrations is the many different ways of doing almost the same striking or kicking technique depending on the style. I always wondered and asked why is this better than that? This was mostly rewarded with push ups and some confusing comment about power or speed.  The good news is there is a universal law of ass kicking; the bad news is unfortunately I can't name it after me as its actually called the Impulse and momentum equation and is derived from Newtons second law: So lets use this awesome law (Ralph's Law of ass kicking :) to answer a common question: What is more important, speed of a punch or amount of weight behind it?

Impulse & Momentum Equation (Universal Law of Ass Kicking)

While this may look scary to many people, most martial artists and boxers know concepts which in practice approximate this equation. The F term is force, the m is mass, the v means velocity (think speed with direction) and the t is time. The funny triangle actually means "change in". So the top line on the right side of the equation means mass times the change in velocity (change in momentum), and the bottom means change in time (really translates into the time it took for the change in momentum). This equation actually tells you if we have a mass travelling at a certain velocity with a given mass (think kilograms or pounds if you are metrically disabled) and it impacts with something for a period of time and is slowed down to a final velocity the impact force it imparts is F. So what does this really mean: if we want to increase our impact force when striking someone we can control 3 things, how much mass we have moving, how much change in velocity we can generate and the one most overlooked is controlling the time of impact. Ever wonder why you are often told to retract punches or kicks as quick as possible? Its to make the time of impact as small as possible. If we take a look at the formula, halving the time of impact doubles the impact force. But the formulae works both ways, it can also help you reduce the force of an opponents strikes. Boxers use this concept when they slip with a punch, if the opponent hits them while slipping they have reduced the impact velocity a small amount which reduces impact force a small amount, but by moving in the same direction as the strike they increase the time of impact; so much so that if they can double the time of impact they halve the impact force. This would be the equivalent of making the opponents punch half the speed or halving the weight he has in a punch. Imagine reducing a 100Kg sluggers punch to that of a 50Kg slugger, that's an awesome capability, especially if you are at a weight and reach disadvantage.  
 
So have I convinced you that physics and maths might be useful for martial arts / Self defence (other than repelling psychotic super hot chicks)? The remainder of this chapter will go into detail about where this universal law of ass kicking comes from and how we can use it to derive simple principles and concepts which can enable you to analyse and improve any technique (without a calculator or massively swollen forehead). If you are an instructor it should also allow you to verbalise and better explain principles and concepts which you have already learnt through repetition and "feel". As you progress through this chapter you will probably find your self saying "yes that's so obvious" and that is a good thing; hopefully we will progress (yes me included) to areas where its not so obvious and you get to practice some techniques and experiment for your self. I will hopefully get my work rate up and also complete some practical video tutorials to complement this material.

Objectives:
In this section we will:
- Introduce the basic terminology of force and motion
- Define Newtons three law of force and motion
- Discuss the applications of these laws and develop some concepts and principles which can be applied to martial arts.
On completing this section you will have a basic understanding of the meaning of force and motion and be able to apply this knowledge to:
- Increase or decrease force of impact when striking or blocking
- Evaluate yours and your opponents strengths and weaknesses and apply force and motion concepts to negate or even use   your opponents strengths against him.

Prerequisites:
Before moving into this section you should:
- Understand the concepts of stability, balance and mobility particularly the concepts for centre of gravity (CoG)  and Base of Stability (BoS). If you are not sure what these mean please revise that in the previous theory module: "Balance: Stability and mobility"
- Have a basic knowledge of OODA loop and cognitive functions (implicit and explicit response), this can be revised in the theory module: "Training and Response".

Vector vs. Scalar Quantities

One of the most important things to consider is the difference between a vector and a scalar quantity; a scalar only has magnitude, but a vector has both magnitude and direction. To put this in practical terms consider two types of punch; the "gronk punch" (haymaker) and that of a seasoned boxer. The gronk punch is generally thrown with a big wind up and has massive speed and almost no direction other than at the general target. A good punch however has both speed and specific direction, it will hit the target area as square on as possible transferring as much force as possible to a very specific target. If the gronk gets lucky he will hit the object (maybe a head if he is lucky) with lots of speed but without a specific direction it may be a glancing blow or worse an impact angle which does more damage to himself by breaking bones in the hand.  
Vector Addition
As vectors have both magnitude and direction they can add or subtract in meaningful ways. As an example lets consider a case in one dimension to start with. Consider the example of me throwing a ball: I stand still and throw the ball as hard as possible and it hits a wall in front of me at 10 meters per second.

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